The Seaweed Trail

Mapmakers once thought the earth was flat. Astronomers used to believe the sun circled the earth. As late as the 1990s, archaeologists were convinced that the original American settlers crossed a land bridge from Asia into Alaska, found daylight between the glaciers, and gradually followed it south. According to what had been orthodox thinking, that happened about 12,000 years ago.

“Suppose it were true,” says Jack Rossen, associate professor and chair of the Department of anthropology. “Suppose you could find a corridor through a mile-high wall of ice and follow it for a thousand miles. What would you eat? Popsicles?”

Rossen offers a practical alternative.

“There are seaweed belts along the western coast of the Americas, from Alaska to Chile, and they’re as ecologically complex as rain forests,” he says. “There are canopy species of animals, species of animals beneath the canopy, including fish, and there’s the seaweed itself, which is incredibly rich in nutrients. What would people rather do? Try to find a meal in a world of ice, or take a boat down the coast and help themselves to fish, oysters, and greens?”

In retrospect, the seaweed trail makes sense. But as recently as 15 years ago, it was archaeological heresy to think that North and South America’s first humans didn’t use the land route. The evidence for that conventional wisdom came from a site excavated in the 1930s near what is now Clovis, New Mexico. According to carbon dating, the stone spear points discovered there were 11,200 years old, making Clovis the oldest known settlement in the Americas. The assumption was that hunter-gatherers from Asia had hiked south from the Bering land bridge, living off the occasional mastodon and whatever else they could find.

But in 1975 a visiting veterinary student came across what he thought was a cow bone exposed along a creek bed in southern Chile, some 50 miles from the Pacific coast. When the “bone” turned out to be a mastodon tusk, Tom Dillehay, a renowned archaeologist then at the University of Kentucky (now at Vanderbilt University), and his Chilean colleagues realized they had a prehistoric site on their hands. In 1976 the Dillehay team began an excavation project in Monte Verde, Chile, that would occupy them for the next nine years. In 1983 Dillehay asked one of his dissertation advisees — Jack Rossen — to join the dig.

“He wanted me along because I knew how plant use among ancient cultures — both as food and medicine — reveals how those communities are organized,” Rossen says. “That background was important at Monte Verde because Tom knew the site was going to contain a fair amount of preserved plant life.”

“A fair amount” turned out to be 72 different kinds of plants, including seeds, nuts, berries, and a specimen of wild potato carbon dated at 13,000 years old. “That kind of abundance,” says Rossen, “is unheard of in archaeological science.”

In addition to the plants, Dillehay’s team found a 20-foot long tentlike structure of wood and animal hides, a human footprint small enough to be a child’s, two outdoor hearths, more than 700 finely crafted bone and stone tools, and hundreds of other artifacts.

Not only was the abundance of the findings extraordinary, so was their state of preservation. Normally, plants and other organic materials break down over time, but fallen logs had dammed the creek along which the settlement was founded. Peat moss began building up, and within months the site turned into a bog and had to be abandoned. An air-tight insulator, the peat kept biodegradable material from decaying. Dillehay and his researchers found themselves excavating a mummified village.

That attention to detail paid off. On the floor of what had been a wishbone-shaped structure, Rossen and his colleagues uncovered scatterings of bite-sized lumps shaped like half moons.

“The wishbone structure was most likely a medicine hut,” Rossen says. “And the lumps turned out to be chewed cuds containing five species of seaweed mixed with a variety of purgatives, antibiotics, and other medicinal plants.”

That was remarkable, Rossen says, because at the time of its habitation, Monte Verde was 50 miles from the nearest seacoast. More remarkable: some of the seaweed was from rocky coasts, some from sandy coasts, and some of the plants came from as far as 250 miles away. Even more remarkable: the array of plants included species that weren’t available year-round. They’d been harvested at different times of the year.

“That’s how we know the people who settled Monte Verde stayed there all year long,” Rossen says. “That also tells us they weren’t colonizers because people who are just settling into a place don’t have detailed knowledge of their surroundings. Nor do they have the kinds of established social and trade networks that can bring in plant species from remote locations. The people who lived at Monte Verde had been there a while.”

How long was “a while”? According to the carbon-dated objects at the site, at least 12,500 years. Aha! A human settlement was thriving in southern Chile 500 years before the first settlers were supposed to have crossed a land bridge 10,000 miles to the north.

“Finding a site older than Clovis was a complete paradigm shift, and a lot of people didn’t want to go along with it,” Rossen says. “Showing that humans had been living in the Americas a lot longer than anyone imagined was very controversial and required a very high standard of proof.”

That standard included a 1,000-page research report circulated among leading archaeologists. For years, experts scrutinized the data from the Monte Verde digs, and in 1997, after what Pulitzer Prize–winning journalist John Noble Wilford called “a pitched intellectual battle. . . over when people first inhabited the Americas,” a team of archaeologists sponsored by the National Geographic Society and Dallas Museum of Natural History visited the site. The report they issued vindicated the findings at Monte Verde.

“Monte Verde is real,” wrote Alex W. Barker, chief curator of the Dallas Museum of Natural History. “It’s old. And it’s a whole new ball game.”

Since then, about 25 sites — including two in Brazil and another on an island off the California coast — have been discovered that also predate Clovis. In addition, objects from a deeper layer at Monte Verde have been carbon dated to be nearly 33,000 years old. In other words, people were established in South America almost 22,000 — not just 1,300 — years before Clovis.

In case anyone’s still not totally convinced, evidence from those digs in the 1980s is still coming in. In the May 2008 issue of Science, an article coauthored by Dillehay, Rossen, and others presented a recently completed studyof nine species of seaweed found at MonteVerde, including microscopic particles ingrained along the edge of a stone tool. The study confirmed the original findings.

“Originally, we collected more material than we had time to study,” Rossen says. “But archaeological projects never end. The analysis continues years after the excavations are done. There’s always something more you can do with the material.”

Though archaeologists are now convinced of the coastal route, they’re still sorting out the details. For example, where and how did those early hunter-gatherers stop floating down the coast, foray inland, and settle? It’s hard to tell, since sea levels have risen over the millennia. Sites where ancient people could have established coastal communities are now 200 feet under water. The step-by-step movements of ancient Americans may never be precisely mapped, but Rossen isn’t discouraged.

“Knowing how these people lived is more important than knowing every detail of how they got there, because ancient peoplehave a lot to teach us,” he says. “During 99 percent of our history, humans have been hunter-gatherers — or more accurately, gatherer-hunters — and we’re still that way at heart. We may live in large cities, but we still function best in groupings of 15 to 20 people. And the way we run errands — finding where the bargains are, who has the best service, where the best food is — replicates the behavior patterns of people who know where to go when potatoes are in season, where the best wood is, and which berries to pick.”

Ancient people can also teach us a thing or two about medicine.

“Some of the plants we found at Monte Verde are currently being used in commercial cough syrup,” Rossen says. “Also, because a lot of the food plants used at Monte Verde have an amazingly high nutritional value, those nutrients can treat contemporary people suffering from vitamin deficiencies.”

Among those plants: seaweed.

“Seaweed fills the same nutritional gaps now as it did 20,000 years ago,” Rossen says. “I recommend it. It tastes great.”